Controller output circuit

ABSTRACT

An output drive circuit for a programmable controller includes a triac connected to an a-c power supply in series with a fuse and the controlled external load. The fuse is shunted by a neon indicator lamp and the triac is shunted by a high impedance path including a resistor and capacitor. When the fuse blows and the triac is turned off the the controller, current flows through the neon bulb to indicate the faulty fuse.

United States Patent 1 Struger et al.

11 3,745,546 [451 July 10,1973

[ CONTROLLER OUTPUT CIRCUIT [75] Inventors: Odo J. Struger, Milwaukee;Jay M. Erdman, South Milwaukee, both of [21] Appl. No.1 150,487

3,575,637 4/1971 Krieger et a1. 317/41 X 3,489,927 l/1970 Kellet, Jr. eta1. 1. 317/335 C 3,031,653 4/1962 Bowar et a1 340/250 PrimaryExaminerJohn W. Caldwell Assistant Examiner-Daniel Myer Attorney-BarryE. Sammons and Arthur H. Seidel [5 7 ABSTRACT An output drive circuitfor a programmable controller includes a triac connected to an a-c powersupply in se- [52] US. Cl. 340/250, 337/266 51 rm. Cl. G08b 21/00 a fuseand the Controlled external load- The Field of Search 340/250. 317/40 Afuse is shunted by a neon indicator lamp and the triac 317/335 C 337/79266 241, 332, is shunted by a high impedance path including a resistorand capacitor. When the fuse blows and the triac is [56] ReferencesCited turned off the the controller, current flows through the UNITEDSTATES PATENTS neon bulb to indicate the faulty fuse. 2,697,216 12/1954Lee 340/250 X 5 Claims, 1 Drawing Figure 25 v v Z ;ZZ

co/vTEcuLE/P 2/ Z4 PATENTEIJ 3.745546 com TEOLLE/jg /7 Z/ Z4 INVENTORSODO J. STRUGER JAY M- ERDMAN BY army 6. W

ATTORNEY CONTROLLER OUTPUT CIRCUIT BACKGROUND OF THE INVENTION The fieldof the invention is output drive circuits for use in controllers andparticularly for use in programmable controllers such as that describedin the copending U.S. Pat. application Ser. No. 137,923 of WaveKiffmeyer entitled Programmable Matrix Controller filed Apr. 27, 1971.

Such controllers are connected to sense the condition of various inputdevices, such as limit switches, photocells, push buttons, andsolenoids, and automatically sequence output devices such as motorstarters, lights, control valves and solenoids in accordance withinstructions contained in a stored program. Such a controller might, forexample, control the movement of a part along an assembly line andcontrol the various machines in that line to machine the part.

Although the number of input and output devices vary considerablydepending upon the control function to be performed, the output devices,and hence output drive circuits, may number in the hundreds. The outputdrive circuits are located on printed circuit boards and the necessarynumber of such boards are plugged into the controller and wired to thedevices which they control.

For safety reasons, the controller is adapted to turn off all controlleddevices when a malfunction occurs in any one of them, and due to thelarge number of output devices and associated output drive circuits,troubleshooting such malfunctions becomes very difficult. When themaintenance crew examines a controller which has shut down, it is facedwith the problem of determining which one of possibly hundreds of outputdevices or drive circuits has malfunctioned. Troubleshooting the problemcan be very time consuming and results in a considerable loss inproduction by the machine or machines being controlled.

SUMMARY OF THE INVENTION The present invention comprises an output drivecircuit for a controller which visually indicates a malfunction in thedevice to which it is attached when the controller is shut down. Morespecifically, the invention comprises: an electronic switch connected incircuit with a fuse and with the device to be controlled, high impedancemeans shunting the electronic switch and in circuit with the fuse andcontrolled device, and an indicator lamp connected to shunt the fuse.The electronic switch is actuated by the controller to conduct currentthrough the fuse to the external device. When a malfunction occursblowing the fuse, the controller immediately shuts down, turning off theelectronic switch. A small current continues to flow through theindicator light and high impedance means sufficient in amplitude toilluminate the lamp and indicate the faulty circuit.

An object of the invention is to provide a means of indicating amalfunction in any one ofa number of controller output drive circuits,which means requires a minimal amount of additional hardware to eachoutput drive circuit.

Another object of the invention is to provide a means of indicating amalfunction in an output drive circuit of a controller when theelectronic switch device is turned off by the controller. The highimpedance means shunting the electronic switch provides a conductivepath for current sufficient to illuminate the indicator lamp when thefuse is blown. This small amount of current is insufficient to causefurther damage to the malfunctioning controlled device.

The foregoing and other objects and advantages of the invention willappear from the following description. In the description reference ismade to the accompanying drawing which forms a part hereof, and in whichthere is shown by way of illustration a preferred embodiment of theinvention. The invention may be employed in many different embodiments,and reference is made to the claims herein for interpreting the breadthof the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an electrical schematicdiagram of a controller output drive circuit incorporating the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an outputdrive circuit which embodies the present invention is shown connected tooutput terminals 10 and 11 of a controller 12. As discussed above, thecontroller 12 typically contains a large number of output drive circuitslike that shown in FIG. 1, each output drive circuit being contained ona printed circuit board and the boards being arranged in banks. Eachoutput drive circuit is connected to the controller to receive both anactivate signal and a disabling signal. An activate signal is generatedby the controller 12 when the external device to which a particularoutput drive circuit is attached is to be turned on. The disablingsignal is generated by the controller 12 to turn off all the outputdrive circuits when a malfunction occurs in any one of the controlleddevices.

Referring to FIG. 1, the output terminal 11 of the controller isconnected to a first input terminal 13 of an AND gate 14 and thecontroller output terminal 10 is connected to a second input terminal 15on the AND gate 14. The AND gate 14 is a commercially available logicgate having and output terminal 16 which remains at a logic low untillogic highs are applied to both of its input terminals 13 and 15. Theoutpu terminal 16 of the AND gate 14 is connected through a triggercircuit 27 to the gate terminal of a triac 17. The triac 17 is acommercially available electronic switch which coducts alternatingcurrent when triggered by a signal applied to its gate terminal by thetrigger circuit 27; The trigger circuit 27 may be any one of a number ofsuch circuits known to those skilled in the art. In the instant case,when the output terminal 16 of the AND gate 14 goes high, the triac 17is triggered into conduction by the trigger circuit 27. When the outputtermlnal 16 of the AND gate 14 goes low, however, the triac I7commutates, or turns off when the alternating load current which itconducts passes through zero.

The triac 17 has two load current carrying terminals 18 and l9which areconnected to a high impedance branch comprised of a capacitor 20 andseries connected damping resistor 21. The high impedance path shunts thetriac and is a commonly used arrangement in triac circuits controllinginductive type loads. In such inductive circuits, the current lags thevoltage, and the capacitor 20 is connected to insure commutation of thetriac 17 when the output terminal 16 of the AND gate 14 goes low. Thedamping resistor 21 is added to prevent ringing between the inductiveload and the capacitor 20. A typical value for the capacitor 20 is 0.1mfd. and a typical value for the damping resistor 21 is 100 ohms.Although the high impedance path around the triac 17 is common for thepurpose of insuring commutation of the triac 17, it will be seen fromthe discussion below that this high impedance path provides an entirelydifferent function in the operation of the circuit of the presentinvention.

The triac 17 is connected in series with both a fuse 22 and a load 23 toan a-c power source 24. A neon indicator lamp 25 is connected in serieswith a resistor 26 to shunt the fuse 22. The value of the fuse 22 ischosen to protect the triac 17 and the load 23. The neon type indicatorlamp 25 is chosen because of its low conduction current whenilluminated. Physically, the indicator lamp 25 is located on the printedcircuit board to which the output drive circuit is attached and in aposition readily visible to maintenance personnel.

Under normal operating conditions, the controller output terminal ishigh and activate signals are generated at the output terminal 11 toactuate the triac 17. Thus, when the output terminal 11 is high, theoutput 16 of the AND gate 14 is high and the triac 17 is triggered toconduct alternating current from the a-c power source 24, through thefuse 22 to the load 23. If a malfunction occurs in the controller 12, orone of its other output drive circuits, a disabling signal is generatedat the controller output terminal 10. This disabling signal drives theAND gate input terminal 15 low, causing its output terminal 16 to go lowand thus turn off the triac 17. A small trickle current continues toflow through the fuse 22, damping resistor 21, capacitor 20 and load 23,however, because of the high impedance of capacitor 20, this tricklecurrent is not sufficient to operate the load 23. Also, because the fuse22 has a low impedance, an insignificant voltage drop is developedacross it by this trickle current and the indicator lamp is notilluminated.

lf, on the other hand, a malfunction occurs in the load device 23causing an overload current to flow in the output drive circuit, fuse 22is opened and the controller l2 shuts down by generating a disablingsignal at the output terminal 10. Trickle current again continues toflow through the damping resistor 21 and capacitor 20, however, thiscurrent now flows through, and causes the indicator lamp 25 toilluminate. Thus, the source of the malfunction which caused thecontroller 12 to shut down is immediately identified by the illuminatedindicator lamp 25.

lt should be apparent to those skilled in the art that numerous types offuses 22 can be used in the output drive circuit, and that electronicswitching devices other than triacs can be used. or example, switchingtransistors, SCRs, or relays can be substituted for the triac 17 tocontrol current flow to the load 23. Also, the high impedance patharound the electronic switching device may be varied to accommodate theparticular switching device and the power source used. For example if ad-c power supply is used in combination with a switching transistor, aresistor of high value could be substituted for the daming resistor 21and capacitor 20. Also, in such a case the high impedance path can alsoshunt the load 23, thus providing indication even when the load opencircuits due to the overload current. The

high impedance means in the preferred embodiment shown serves a dualpurpose requiring that it be connected directly to the triac terminals18 and 19, however, absent this constraint it may be connected to shuntboth the triac 17 and load 23. pg,6

We claim:

1. In an output drive circuit for a controller which is connectable to aload to supply current thereto, the combination comprising:

an electronic switch having an input terminal connected to thecontroller and a pair of load current carrying terminals connected toconduct load current to said load when an actuate signal is receivedfrom said controller;

a fuse connected in series with said electronic switch to conduct saidload current; high impedance means connected in shunt relation to saidelectronic switch to conduct a small amount of said load current whensaid electronic switch is non-conductive; and

an indicator lamp connected in shunt relation with said fuse;

wherein the high impedance means conducts sufficient current toilluminate said indicator lamp when said electronic switch isnon-conductive and said fuse is open circuited.

2. The output drive circuit of claim 1, which includes a logic gatehaving an input terminal connected to the controller and an outputterminal conneted to said electronic switch input terminal, said logicgate being operable to prevent application of the actuate signal to saidelectronic switch when a disabling signal is received at said gate inputterminal from said controller.

3. The output drive circuit of claim 1 wherein said electronic switch isa triac and said high impedance means is a series connected resistor andcapacitor connected to said load current carrying terminals.

4. In a controller having a plurality of output drive circuits, each ofsaid output drive circuits containing an electronic switch having acontrol terminal connected for operation by said controller, and a pairof load current carrying terminals connected to conduct load current toan external load connected to said controller, the improvement in saidoutput drive circuits comprising:

a fuse connected in series with said electronic switch to conduct loadcurrent;

high impedance means connected in shunt relation with said electronicswitch; and

an indicator lamp connected in shunt relation with said fuse;

wherein a trickle current flows through said high impedance means whensaid electronic switch is nonconductive, and said trickle current flowsthrough said indicator lamp when said fuse is open circuited toilluminate the same and provide a visual indication when said fuse openscircuit.

5. A circuit as recited in claim 4 in which a logic gate is connected tothe control terminal of said electronic switch and said logic gateincludes an input terminal connected to receive a disabling signal fromsaid con-

1. In an output drive circuit for a controller which is connectable to aload to supply current thereto, the combination comprising: anelectronic switch having an input terminal connected to the controllerand a pair of load current carrying terminals connected to conduct loadcurrent to said load when an actuate signal is received from saidcontroller; a fuse connected in series with said electronic switch toconduct said load current; high impedance means connected in shuntrelation to said electronic switch to conduct a small amount of saidload current when said electronic switch is non-conDuctive; and anindicator lamp connected in shunt relation with said fuse; wherein thehigh impedance means conducts sufficient current to illuminate saidindicator lamp when said electronic switch is non-conductive and saidfuse is open circuited.
 2. The output drive circuit of claim 1, whichincludes a logic gate having an input terminal connected to thecontroller and an output terminal connected to said electronic switchinput terminal, said logic gate being operable to prevent application ofthe actuate signal to said electronic switch when a disabling signal isreceived at said gate input terminal from said controller.
 3. The outputdrive circuit of claim 1 wherein said electronic switch is a triac andsaid high impedance means is a series connected resistor and capacitorconnected to said load current carrying terminals.
 4. In a controllerhaving a plurality of output drive circuits, each of said output drivecircuits containing an electronic switch having a control terminalconnected for operation by said controller, and a pair of load currentcarrying terminals connected to conduct load current to an external loadconnected to said controller, the improvement in said output drivecircuits comprising: a fuse connected in series with said electronicswitch to conduct load current; high impedance means connected in shuntrelation with said electronic switch; and an indicator lamp connected inshunt relation with said fuse; wherein a trickle current flows throughsaid high impedance means when said electronic switch is nonconductive,and said trickle current flows through said indicator lamp when saidfuse is open circuited to illuminate the same and provide a visualindication when said fuse opens circuit.
 5. A circuit as recited inclaim 4 in which a logic gate is connected to the control terminal ofsaid electronic switch and said logic gate includes an input terminalconnected to receive a disabling signal from said controller.